The present invention relates to the recovery of a solid polymer from a liquid-solids slurry. In another aspect, the present invention relates to the polymerization and recovery of polymers of mono-1-olefins. In yet another aspect, the present invention relates to the recovery and reuse of polymerization diluent.
Various reactions for polymerizing mono-1-olefins are described in the literature, and the polymerizations are usually carried out in the presence of catalysts. In particular preferred processes, the polymerization is conducted under such conditions that the polymerization effluent comprises a liquid-solids slurry. Typically, in such processes, the polymerization effluent comprising solid polymer and liquid diluent is subjected to a washing step. In the washing step, the polymer solids are contacted with a wash liquid which aids in separating the catalyst residue from the polymer. The wash liquid containing catalyst residue and catalyst extractant, if employed, is separated from the polymer and subjected to purification so that it can be reused. The solid polymer is then passed to a flash zone wherein liquid that is associated with the polymer is removed by being flashed to vapor and the solid polymer is recovered. Examples of such processes are disclosed in U.S. Pat. Nos. 3,219,647; 3,324,093; 3,280,090; 3,285,899; and 3,454,545, the disclosures of which are incorporated herein by reference.
Typically in such processes in the past, the wash liquid and the vapors from the flash zone have been sent to a fractionation zone wherein diluent, which is often the same as both the monomer and the wash liquid, is purified and recycled for reuse in the process. Generally, the wash liquid and the vapors from the flash zone have been passed to the same fractionation zone and a portion of the fractionator overhead has been condensed and used as wash liquid.
An object of the present invention is to provide a method of reusing the wash liquid which can result in very significant utility savings.
Still another object of the present invention is to provide a process for recovering polymer and diluent which can use less expensive fractionation equipment than must be employed when both the wash liquid and the flash vapors are subjected to fractionation.
In yet another aspect the present invention provides an integrated process which can result in a reduction in the losses of monomer that occur during the further steps invovled in recovering the polymer.